How to Read Decimal Fractions in Russian

Some say it's possible to read 32.1 as тридцать два и одна
it's ok to read 5.6 as пять и шесть?
how about really long numbers such as 1.23456? the formal way "одна целая двадцать три тысяч..." is way too long

Yes, you can say 32.1 as тридцать два и одна, but it is correct to say тридцать две целых одна десятая. However, when we speak about person's temperature, we would say тридцать шесть и шесть, тридцать семь и одна, etc.